Abstract: Idiomorphic grains of zircon from the Huangcaoshan and Xiasuozi granites in the western margin of Yangtze plate were analyzed by using the　206Pb-235U mixed dilution technique. The results show that U-Pb ages of zircons from the Huangcaoshan granite are variable. The apparent-age relationship t207/206>t207/235>t206/238 is evident for these zircons, indicating that the difference in apparent ages for different grains is caused by radiogenic Pb loss in different degrees. In the concordance diagram, the lower intercept age of 786±36 Ma represents the crystallization age of the zircon; the upper intercept age of 195±78 Ma may be interpreted as the age of heat event causing the radiogenic Pb loss. Differing from the Huangcaoshan granite, there is no difference in the apparent ages of zircons from the Xiasuozi granite within the analytical error. In the concordance diagram, the data-points are all plotted on the concordance line, indicating that U-Pb isotopic system remains closed after crystallization of zircons. Therefore, the concordance age of 805±15 Ma may represent the crystallization age of zircons. 　　The above-mentioned results show that the Huangcaoshan and Xiasuozi granites were the products of Jinning period magmatism, and the important components of the Jinning orogenic belt around the Yangzte plate.